Molecular tunnel junctions and their use as sources of electronic plasmons

Abstract

A method of producing electronic plasmons by applying a bias to a molecular tunnel junction to excite plasmons, in which the molecular tunnel junction contains a top metallic electrode formed of a eutectic metal alloy and a metal oxide, a bottom metallic electrode formed of a transition metal, and a self-assembled monolayer formed of a plurality of organic molecules disposed between the top metallic electrode and the bottom metallic electrode. Also disclosed are a molecular tunnel junction for producing electronic plasmons and a method for preparing such a molecular tunnel junction.

What is claimed is: 
     
       1. A method of producing electronic plasmons, the method comprising:
 providing a molecular tunnel junction, 
 applying a bias to the molecular tunnel junction to excite plasmons, and 
 detecting the plasmons thus produced, 
 
       wherein the molecular tunnel junction contains a top metallic electrode formed of a eutectic metal alloy and a metal oxide, a bottom metallic electrode formed of a transition metal, and a self-assembled monolayer formed of a plurality of organic molecules disposed between the top metallic electrode and the bottom metallic electrode. 
     
     
       2. The method of  claim 1 , wherein the plurality of organic molecules each contain a —SR thiolate moiety, in which R is a molecular chain formed of an alkyl group, an alkynyl group, an aryl group, a heteroaryl group, a metallocene group, a redox-active group, an optically active group, or a combination thereof. 
     
     
       3. The method of  claim 2 , wherein the SR thiolate moiety contains an alkyl chain. 
     
     
       4. The method of  claim 3 , wherein the —SR thiolate moiety is —S(CH 2 ) n-1 CH 3 , n being 10, 12, 14, 16, or 18. 
     
     
       5. The method of  claim 2 , wherein the plurality of organic molecules are a plurality of molecular diodes each formed of a —SR thiolate moiety, in which R is a molecular chain containing an aryl group, a heteroaryl group, or a metallocene group; and the plurality of molecular diodes enable bias selective plasmon excitation. 
     
     
       6. The method of  claim 5 , wherein the —SR thiolate moiety is 
       
         
           
           
               
               
           
         
       
     
     
       7. The method of  claim 1 , wherein the molecular tunnel junction contains a self-assembled monolayer formed of a plurality of molecular diodes that enable either direct plasmon excitation or directional plasmon excitation. 
     
     
       8. The method of  claim 1 , wherein the plasmon excitation is enabled via direct quantum mechanical tunneling. 
     
     
       9. The method of  claim 1 , wherein the plasmon excitation has a metal-insulator-metal surface plasmon polariton (SPP) mode, a surface propagating plasmon mode, or a localized surface plasmon mode. 
     
     
       10. The method of  claim 1 , wherein the plurality of organic molecules enable direct propagating SPP excitation by using a gold strip bottom electrode. 
     
     
       11. The method of  claim 1 , wherein the plurality of organic molecules enable direct plasmon excitation or directional plasmon excitation by using a gold waveguide bottom electrode. 
     
     
       12. The method of  claim 1 , wherein the plurality of organic molecules enable bias selective plasmon excitation via direct quantum mechanical tunneling. 
     
     
       13. The method of  claim 12 , wherein the bias selective plasmon excitation has a metal-insulator-metal SPP mode, a surface propagating plasmon mode, or a localized surface plasmon mode. 
     
     
       14. The method of  claim 1 , wherein the top metallic electrode is formed of a eutectic metal alloy and a metal oxide, in which the eutectic metal alloy is EGaIn and the metal oxide is Ga 2 O 3 . 
     
     
       15. The method of  claim 1 , wherein the bottom metallic electrode is formed of a transition metal selected from the group consisting of Au, Ag, Cu, Ni, Pt, and Pd. 
     
     
       16. The method of  claim 1 , wherein the plurality of organic molecules each contain a —SR thiolate moiety, the —SR thiolate moiety being covalently bond to the bottom metallic electrode through a metal-thiolate bond and being non-covalently bond to the top metallic electrode through van der Waals interactions. 
     
     
       17. The method of  claim 1 , wherein the plasmon excitation is enabled via directional tunneling that is modulated by the tilt angle of the self-assembled monolayer with respect to the bottom metallic electrode. 
     
     
       18. The method of  claim 17 , wherein the tilt angle is modulated by interactions between the plurality of organic molecules and the bottom metallic electrode. 
     
     
       19. The method of  claim 17 , wherein the self-assembled monolayer has a tilt angle of 10°-30°, inclusive, with respect to the bottom metallic electrode. 
     
     
       20. A molecular tunnel junction for producing electronic plasmons, comprising:
 a top metallic electrode formed of an eutectic metal alloy and a metal oxide, 
 a bottom metallic electrode formed of a template-striped metal, and 
 a self-assembled monolayer formed of a plurality of molecular diodes disposed between the top metallic electrode and the bottom metallic electrode, 
 
       wherein the plurality of molecular diodes each contain a —SR thiolate moiety, in which R is a molecular chain containing an aryl group, a heteroaryl group, or a metallocene group, and an alkynyl group; and the plurality of molecular diodes enable bias selective plasmon excitation. 
     
     
       21. The molecular tunnel junction of  claim 20 , further comprising an optical adhesive layer and a substrate layer, the substrate layer attached to the bottom metallic electrode via the optical adhesive layer. 
     
     
       22. The molecular tunnel junction of  claim 20 , wherein the top metallic electrode is formed of a eutectic metal alloy and a metal oxide, in which the eutectic metal alloy is EGaIn and the metal oxide is Ga 2 O 3 . 
     
     
       23. The molecular tunnel junction of  claim 20 , wherein the bottom metallic electrode is formed of a transition metal selected from the group consisting of Au, Ag, Cu, Ni, Pt, and Pd. 
     
     
       24. The molecular tunnel junction of  claim 20 , wherein the plurality of molecular diodes each contain a —SR thiolate moiety, the —SR thiolate moiety being covalently bond to the bottom metallic electrode through a metal-thiolate bond and being non-covalently bond to the top metallic electrode through van der Waals interactions. 
     
     
       25. The molecular tunnel junction of  claim 24 , wherein the —SR thiolate moiety is 
       
         
           
           
               
               
           
         
       
     
     
       26. The molecular tunnel junction of  claim 25 , wherein the self-assembled monolayer has a tilt angle of 10°-30°, inclusive, with respect to the bottom metallic electrode. 
     
     
       27. A method of fabricating a molecular tunnel junction of  claim 20 , the method comprising:
 providing a bottom metallic electrode formed of a template-striped metal, 
 depositing onto the bottom metallic electrode a plurality of molecular diodes to form a self-assembled monolayer, and 
 forming a top metallic electrode onto the self-assembled monolayer, 
 wherein the plurality of molecular diodes each contain a —SR thiolate moiety, in which R is a molecular chain containing an aryl group, a heteroaryl group, or a metallocene group, and an alkynyl group; and the plurality of molecular diodes enable bias selective plasmon excitation without the need of an optical element.